B. J. Skromme

Effects of passivating ionic films on the photoluminescence properties of GaAs

The passivating effects of spin‐coated films of Na2S⋅9H2O on GaAs surfaces have been studied using room‐temperature photoluminescence (PL) and low‐temperature PL spectroscopy. After passivation, the 300 K PL efficiency is increased on both n‐ and p‐type material; improvements of up to 2800× are observed. The surface field and surface recombination‐related notch features in the free and bound exciton emission spectra at low temperature are eliminated, implying that the residual band bending under illumination is less than 0.15 V.

Growth of high‐quality GaAs using trimethylgallium and diethylarsine

In this letter we report the growth of high‐quality gallium arsenide using trimethylgallium and diethylarsine. The epitaxial layers had excellent morphology, an n‐type background free‐carrier concentration as low as 3×1014 cm−3 and a liquid nitrogen temperature mobility as high as 64u2009600 cm2/Vu2009s. The low‐temperature (2 K) photoluminescence spectrum has well‐resolved excitonic peaks, confirming the high quality of the material.

Band bending, Fermi level pinning, and surface fixed charge on chemically prepared GaAs surfaces

We compare the nature of the band bending under GaAs surfaces prepared by alkaline sulfides [Na2S⋅9H2O, (NH4)2S] with that under oxidized GaAs surfaces. We make the point that Fermi level pinning implies band bending, but band bending does not necessarily imply ‘‘pinning.’’ In either case, even weak light illumination substantially flattens the bands. On ammonium sulfide treated surfaces the fixed and trapped charge density in the dark is only ∼5×1011 electrons/cm2, but these few states are mostly neutralized at low‐level forward injection. This behavior should not be confused with Fermi level pinning.

InGaAs/InP superlattice mixing induced by Zn or Si diffusion

Recent studies have shown that Zn diffusion preferentially induces mixing (interdiffusion) of In and Ga in unstrained InGaAs/InP superlattices, with little diffusion of the anions. In the present study, a 3.1% lattice mismatch is accommodated in the mixed superlattice with no observable defects in layers on the order of the predicted critical layer thickness. At high concentrations, Zn resides preferentially in the InP layers in the form of Zn3P2. In marked contrast to this behavior of Zn, Si diffusion is observed to cause comparable interdiffusion on the cation and anion sublattices within a narrow range of dopant concentration. This result is at odds with some recent mixing models and is consistent with a divacancy mixing mechanism.

Planar doping with gallium of molecular beam epitaxial ZnSe

A new approach to doping in ZnSe, which involves Ga deposition in spatially separated atomic planes (planar doping), is reported. The dependence of doping efficiency on the particular surface termination (Zn or Se stabilized) maintained during the deposition of the Ga dopant is investigated by Hall measurements and low‐temperature photoluminescence spectroscopy, and the results are compared to those obtained for uniform doping. Under our growth conditions and for the same average amount of Ga atoms arriving at the ZnSe surface, the doping efficiency is dramatically enhanced in the case of Ga planar doping on Zn terminated surfaces. This enhancement correlates with the reduction of the broad deep luminescence bands that dominate under the other doping conditions, indicating an effective reduction of the self‐compensating mechanisms. Under optimized conditions, n‐type ZnSe with carrier concentration in the 1018 cm−3 range is achieved.

Arsenic doped ZnSe grown by molecular‐beam epitaxy

We have been able to incorporate As into molecular‐beam epitaxy (MBE) grown ZnSe in the range of 1017–1021 atoms/cm3 using Zn3As2 as the As source. This contrasts with very low As levels we obtained using an As cracker cell. The As incorporation is highly nonlinear with Zn3As2 flux and depends on the excess Se used. Several samples doped with Zn3As2 show low temperature photoluminescence with near band edge emission dominated by shallow acceptor levels. We will describe the details of several growth variations studied and their influence on As incorporation.

Photoluminescence characterization of ZnSe doped with Ga by bulk and planar doping techniques in molecular‐beam epitaxy

Room‐temperature and low‐temperature (1.7‐K) photoluminescence (PL) characteristics of heteroepitaxial ZnSe layers on GaAs which are doped with Ga by either conventional (bulk) or planar doping techniques are described. Low‐temperature PL peaks at 2.27 and 2.0 eV involving deep acceptor levels are introduced by Ga doping, as well as newly reported shallow acceptor levels with binding energies of approximately 68 and 85 meV. The behavior of these peaks and the excitonic transitions is studied as a function of Ga‐doping level and, for the case of the planar‐doped layers, surface stoichiometry during doping. The exciton peaks exhibit substantially greater broadening for doping on Zn‐rich surfaces than for Se‐rich surfaces, corresponding to the higher carrier concentrations observed by electrical measurements in the former case. The deep acceptor levels are found to be incorporated to a lesser degree for doping on Zn‐rich surfaces, while the incorporation of the 85‐meV acceptor is enhanced in this case. The n...

Atomic layer epitaxy of device quality GaAs

Device quality GaAs was grown in a conventional organometallic chemical vapor deposition reactor, using sequential group III (trimethylgallium, TMG) and group V (arsine) reactant gas exposures typical of atomic layer epitaxy (ALE). The results show that, at a given temperature, impurity (e.g., carbon) incorporation is controlled by the effective V/III ratio at the growing surface, which is determined by the sequence used in the growth cycles. This effect, specific to ALE, is quantified by solving the diffusion equation that describes concentration transients at the growing surface. Detailed photoluminescence experiments identified C and Mg as the residual acceptors and Ge as the sole residual donor in a 3×1015 cm−3 n‐type background layer with mobilities of 5600 cm2/Vu2009s at room temperature and 35u2009000 cm2/Vu2009s at 77 K. A higher purity sample showed reduced levels of Ge, with traces of S, Si, and Te donors and only C acceptors.

Surface stoichiometry effects on ZnSe/GaAs heteroepitaxy

Abstract We describe a simple model, based on counting of valence electrons at the interface, which can predict the surface reconstructions which provide optimal heteroepitaxial growth. Vertical photocurrent measurements on a series of ZnSe/GaAs heterostructures grown by molecular beam epitaxy, using various GaAs surface reconstructions, support the model predictions that surfaces which provide nearly equal number of the constituent atoms for interface bonds produce the highest quality interfaces.

Arsenic‐doped P‐type ZnTe grown by molecular beam epitaxy

Efficient p doping of ZnTe by arsenic has been achieved using a Zn3As2 effusion cell. Doping levels of ZnTe/GaAs can be controlled from 1016 to 1018 cm−3. The carrier concentration is independent of the substrate used, ZnTe:As/GaAs and ZnTe:As/InP giving similar results. Spectral photoconductivity and low‐temperature photoluminescence, however, show an increase of deep levels for doping levels higher than 1017 cm−3 but electrical measurements show no saturation for doping as high as 1018 cm−3.